This invention relates to a bicycle frame based on the main concept specified in claim 1.
Bicycle frames are exposed to severe strain and stress under the most diverse operating conditions and must therefore be built with a high degree of sturdiness and rigidity. This applies collectively to all tubular sections, braces and brackets making up the frame as well as to the connections between the preferably tubular braces.
Accordingly, it is the objective of this invention to introduce a way to further enhance the sturdiness and rigidity of a bicycle frame.
A solution toward achieving the objective of this invention is offered by a bicycle frame as specified in claim 1.
It provides for the bicycle frame to incorporate a one-piece, forked chain bracket produced from a fiber-reinforced polymer material.
The chain bracket or fork preferably consists of a fiber-reinforced, at least partly cross-linkable polymer. The fibers employed are carbon fibers, mineral fibers, metal fibers or high-quality polymer fibers such as aramide fibers.
The chain fork is preferably shaped with the two legs of the fork curved outward as viewed from the crank bearing toward the rear-wheel axle while next to the crank bearing these two bracket legs connect into a single unit.
At the crank-bearing end the chain fork features a male adapter section designed for the plug-in connection with a receptacle provided in or on the crank enclosure.
The chain fork, i.e. its two bracket legs, and the aforementioned adapter section are preferably configured as hollow, tubular elements.
As another proposed feature a pedal crank enclosure is provided which incorporates the aforementioned receptacle for accepting the adapter section of the chain fork.
As another proposed feature the pedal crank enclosure is provided with at least one and preferably two support surfaces or support consoles on which the saddle-pillar tube and, where appropriate, the bottom tube of the frame, butting at an oblique angle, are welded to the pedal crank enclosure. This angled junction of both the saddle-pillar tube and the bottom frame tube with the said support surface or support console results in a longer welded seam which increases the rigidity of the connection with the crank enclosure.
Toward the end facing the rear-wheel axle of the bicycle the two bracket legs of the chain fork are each provided with a socket permitting their connection to the rear-wheel axle for instance via a metal adapter.
The pedal crank enclosure, preferably consisting of a metal such as aluminum, and the chain fork, consisting of a fiber-reinforced polymer, are solidly cemented together.
The characteristic features of other preferred design variations of the bicycle frame according to this invention are specified in the subordinated claims.